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Andrea Soddu

eV Seesaw with Four Generations and 3+3 scenario. Andrea Soddu. Weizmann Institute of Science. ICHEP06. Wei-Shu Hou, A.S. July 26 – August 2, 2006. Phys. Lett. B 638, 2006. Russian Academy of Sciences. Moscow. Outlook.

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Andrea Soddu

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  1. eV Seesaw with Four Generations and 3+3 scenario Andrea Soddu Weizmann Institute of Science ICHEP06 Wei-Shu Hou, A.S. July 26 – August 2, 2006 Phys. Lett. B 638, 2006 Russian Academy of Sciences Moscow

  2. Outlook LSND data and eV-Seesaw Is a forth generation ruled out by EW precision tests? Can a forth generation be embedded in a eV-Seesaw scenario? Decoupling the forth generation 4+4 3+3 Fitting the oscillation data in 3+3

  3. MiniBooNE will be able to prove or disprove LSND anomaly

  4. Additional “sterile” neutrinos involved in oscillations Strong constraints from BBN and CMB If 4He systematic larger BBN constraints can be evaded in Non-Standard Cosmology R. Foot and R. R. Volkas Phys. Rev. Lett. 75, 1995 LSND is not yet ruled out by cosmological observations S. Hannestad JCAP 0305, 2003

  5. After SSB describes 6 neutral Weyl fermions 6 neutrinos The 6 neutrinos “fuse” into 3 Dirac fermions with The 6 neutrinos split up into 3 light mostly active neutrinos and 3 heavy, mostly sterile neutrinos with

  6. LSND results Evidence for flux 30 meters away from a source of neutrinos produced in decay in flight, and the subsequent decay, at rest, of appearance can be explained if eV Seesaw and LSND Andre’ de Gouvea Phys. Rev. D72, 2005 Nothing experimental is really known about the magnitude of M except perhaps the LSND result, which is at eV scale.

  7. eV Seesaw and LSND In the basis where charged lepton mass matrix is diagonal

  8. Is a forth generation allowed ? It is natural to have particles with mass of order EW scale Existence of a 4TH generation: U, D, N, E Existence of a 4TH generation with all fermions heavier than MZ strongly disfavored by EW precision data J. Erler and P. Langacker Phys. Lett. B 592, 2004 What about ? In the Standard See-saw all the four active neutrinos are light 

  9. All EW precision data and mH > 90 GeV at 95 % CL from LEP II were used in the fit S,T,U parameterization valid for mNP >> MZ M. Maltoni, V.A. Novikov, L.B. Okun, A.N. Razanov and M.I. Vysotsky Phys. Lett. B 476, 2000 One and even two generations are allowed when neutral fermions are relatively light N strongly decoupled from the three light neutrinos to avoid constraint from LEP II

  10. 4+4 scheme has 6 zero eigenvalues plus two eigenvalues

  11. 4+4 scheme 3+3 scheme Pseudo-Dirac neutrino N of mass For the six null eigenvalues of one can apply perturbation theory with degeneracy Having started in the basis where is diagonal, one still has the freedom to perform a rotation in the left sector.

  12. 3+1 scheme is the fourth lightest neutrino and oscillations involving the 5th and 6th states do not contribute in any significant way.

  13. 3+3 scheme

  14. 3+3 Mass Matrix Democratic Structure Mass Spectrum 3+3 Rotation Matrix MNS

  15. Upper Corner Solution Lower Corner Solution

  16. Lower Corner Solution

  17. Upper Corner Solution

  18. Conclusions LSND not yet ruled out by MiniBooNE or cosmological observations LSND eV scale could be an indication for the right-handed neutrino scale M eV Seesaw can explain all the oscillations data All EW precision measurements are satisfied with mN = 50 GeV A sequential forth generation is well embedded in a eV Seesaw scenario eV Seesaw with a forth generation can equally fit all the oscillations data

  19. back up

  20. Normal mass hierarchy for the three active neutrinos Too small to explain LSND anomaly

  21. Inverted mass hierarchy for the three active neutrinos

  22. For (3+1) models poor agreement between NSBL and LSND data M. Sorel, J.M. Conrad and M.H. Shaevitz, LSND NSBL

  23. 3+2 scheme Quasi-degenerate neutrino masses

  24. Oblique Parameters S, T, U Adequate when all particles of the forth generation are heavier than MZ M. E. Peskin and T. Takeuchi U=0 (2003) J. Erler and P. Langacker hep-ph/0407097 An extra generation of chiral fermions is excluded at 99.95% CL on the basis of the S parameter alone, if the new doublets are degenerate, T=U=0. For non degenerate doublets T>0. The data currently favor T<0 strengthening the exclusion limit. If the extra neutrino is close to its direct mass limit, S can be small or even negative but at the expense of too large contribution to T

  25. Modified Oblique Parameters S, T, U H.-J. He, N. Polonsky and S. Su hep-ph/0102144 (2000) outside 95% C.L. S-T contour • decrease S • lift up T • achieve both Extra family gives large positive T and in many cases also a sizable S>0 (case ii)

  26. Correlations among the contributions to the three oblique parameters S, T, U rather than the contribution to a particular one, provide the most significant bound. A single extra chiral family with a constrained spectrum is consistent with precision data without requiring any New Physics source

  27. (2005) hep-ex/0509008 A four generation could still be alive and if yes it will appear soon

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